Television transmission system



April 7, 1942. u. KNICK 2,278,788

TELEVISION TRANSMISSION SYSTEM Filed June 14, 1939 2 Sheets-Sheet lINVENTOR BY (/LE/CHK/V CK 3,.

TTORNEY Patented Apr. 7, 1942 UNITED STATES PATENT OFFICE TELEVISIONTRANSMISSION SYSTEM Ulrich Knick, Berlin-Steglitz, Germany, assignor toFernsch Aktiengesellschaft, Berlin-Zehlendorf, Germany Application June14, 1939, Serial No. 279,082

Germany June 14, 1938 5 Claims.

ners are located at considerable and different distances from thetransmitter, it will be appreciated that the returning synchronizingsignals will no longer be in phase with the master impulses or withrespect to each other, due to the various degrees of phase delayincurred by transmission over difl'erent lengths of wire lines.

This is particularly inconvenient in case it is desired to switch fromthe transmission of picture signals supplied from one scanner to that ofsignals from another scanner. It hasbeen proposed to employ phase-delaynetworks in lines arriving from the scanners in order to be able to makethe phase of the synchronizing impulses returning from the differentscanners the same. This method, however, has the great disadvantage thatsuch delay networks, through which the picture signals are also fed,cause appreciable distortion of the latter. Furthermore, such networksmust be carefully and accurately balanced. The danger also exists thatthe constants of such networks are changed by exterior influences suchas temperature, humidity and the like.

It is the object of this invention to overcome the above disadvantages;to provide a method by means of which the synchronizing impulsesreturning from all scanners are made to have the same phase; to providea method by means of which compensation of the phase delay of thesynchronizing impulses due to the transmission over wire linestakesplace before transmission; and to provide a method by means of which thephase correctness can be automatically regulated.

Referring to the drawings, Fig. 1 shows a schematic layout while Fig. 2shows circuit means by way of example for carrying out the invention.

Broadly considered, this invention provides for having available at thetransmitter a master signal, to generate at the transmittersynchronizing signals which are transmitted by wire to the inthat of themaster signal and to regulate the phase of the synchronizing signalgenerator so that the phases of the master signal and of the returningsynchronizing signal are in a predetermined relation, which isthe samefor the syn chronizing impulses returning from all scanners. Thisregulation may be donebyobservatidn and manual readjustment, orautomatically by deriving from the phase comparison a regulating voltageand using this voltage to regulate the phase of the synchronizing signalgenerator.

Thus in this manner the phase delay due to wire transmission iscompensated for before transmission of the synchronizing signals.

The invention shall now be explained more in detail in connection withthe drawings Fig. 1 schematically shows a layout embodying my invention.Central station I may be at the transmitter. This, however, is notnecessary inasmuch as block I indicates the junction point of thecommunication channels to the individual scanners with the commontransmission channel to the wireless transmitter. Thus, block I mayindicate a mixing desk, a switching arrangement or the like. Picturescanners 2, 3 and 4 are located at various distances of considerabledifference from junction point I. Synchronizing impulse generators 8, 9and iii are preferably of the type having a master impulse generator atdouble line-scanning frequency and a number of frequency-dividing stagesby means of which line-synchronizing and framing impulses are derivedfrom this master frequency. Blocks i2, Ho and 12b are means of phasecomparison. The master signal generator H in a preferred embodiment ofthe invention is merely a terminal of the 60-cycle alternating currentpower mains. Leads l3, Ba and l3b connect the respective phasecomparators with their associated synchronizing impulse generators,while wires 5, 5a, 6, 6a, 1 and 1a connect television scanners 2, 3 and4 with their respectiveassociated synchronizing impulse generators andphase comparators.

Thus, Fig. 1 shows three separate scanner channels, each comprising asynchronizing impulse generator, a lead through which synchronizingimpulses are fed to the scanner, a lead through which'the returningsynchronizing impulse ls fed to the phase comparator, a lead feeding themaster signal to the phase comparator,

and a lead feeding the regulating voltage produced by the phasecomparator to the synchronizing impulse generator. Common to all threechannels is the master signal source I l. Prefa is fed to thesynchronizing impulse generator,

thus adjusting the phase of the latter in such a manner that thereturning framing impulses, and thereby also the line-synchronizingimpulses, will be in a different predetermined phase relation with themaster signal. It will be understood that in this manner, by comparingthe returning framing impulse with a master signal of the samefrequency, the phase of the outgoing framing signal produced by thesynchronizing impulse generator is so controlled and advanced to such adegree that the phase delay incurred in wire transmission is compensatedfor at least in part so that the framing impulses returning from allscanners will arrive in the same phase. Inasmuch astheline-synchronizing signals are in a rigid phase relation with theframing impulses if produced by synchronizing generators, as brieflydescribed above, the phase of the line-synchronizing impulses will beshifted in the same manner as that of the framing impulses.

While I have shown in Fig. 1 separate synchronizing impulse generatorsand phase comparators for each television scanner channel, this is notabsolutely necessary. If all synchronizing impulse generators and phasecomparators are identical, it is also possible to operate a system witha multitude of scanners with only two synchronizing impulse generatorsand phase comparators, inasmuch as only one set of apparatus is requiredfor the signals being transmitted by wireless, while the other set isrequired for preparing anotherscanner channel to which it is desired toswitch over. I

Fig. 2 shows, by way of example, in more detail a means for carrying outthe method in accordance with my invention. Block l indicates asine-wave oscillator comprising an oscillator tube It and afrequency-regulating tube I| to which a regulating voltage is appliedthrough lead 3|. It will be understood that any oscillator circuitallowing frequency control by means of a regulating voltage can be usedas well. Oscillator I5 is made to oscillate with double line frequencywhich, according to present standards, is 26,460 cycles. The generatedsine-wave is applied to a device l8, indicated by block diagram only,which converts the sine wave into a square-top wave of the samefrequency. This square-topped wave is fed through a chain of frequencydividers I8, 20, 2| and 22, the output of which is a 60-cyclesquare-topped framing impulse. Such frequencydividing chains are wellknown in the television art and may comprise a plurality ofmultivibrator circuits tuned to different frequencies and eachsynchronized by the preceding impulse generator operating at a higherfrequency. Inasmuch as various devices of this type are well known inthe art, it is not deemed necessary to explain these in further detailas any well-operating chain can be used for this purpose. Theline-scanning frequency is preferably derived from the square toppedimpulses of 26,460 cycles produced by device l8 by means of a frequencydivisiorrof 1 to 2. This is not shown because it is not deemed essentialto the invention. lt will, however, be understood that such a chain willproduce linesynchronizing impulses atfa frequency of 13,230 cycles andframing impulses at 60 cycles which 2,27s,7ss

are in a rigid phase relation with respect to each other.

The output of divider 22, which is a 60-cycle preferably square-toppedframing impulse, is fed through lead 23 to a television scanner 24placed scanner. Line-synchronizing impulses may also be superimposedupon the picture signals and framing signals. The specific way in whichthe framing impulses are returned is not material so long as return lead25 carries returning 60-cycle framing impulses. In case a compositetelevision signal is returned, a synchronizing separator 26 may beprovided, the output of which must be a positive -cycle square-toppedimpulse. In case an auxiliary carrier is made use of, it is, of course,necessary toprovide a rectifier. Such means, being well known in theart, are not believed to require any detailed explanation. The returningpositive 60-cycle framing impulse is then fed to the control grid oftube 28 in phase comparator 21. In the plate circuit of tube 28 there isconnected a transformer primary winding 28 in series with ashunt-connected resistor 32 and smoothing condenser 33. The mastersignal, mentioned earlier in this description with a frequency of 60cycles is fed to the secondary winding 30 ofthe same transformer. Thismaster signal is preferably sinusoidal and can be derived directly fromthe 60-cycle power mains as it is common to interlock the televisionscaning pattern with the alternating-current power mains.

Phase comparator 21 operates as follows: The cathode of tube 28 is sobiased that no plate current can flow in the absence of a positiveSO-cycle square-topped impulse upon the grid. Upon arrival of such animpulse, the tube draws current and a voltage dropis produced acrossresistor 32. The time constant of the shunt combination of 32-33 is sochosen that the voltage across resistor 32 is substantially direct. Itis, of course, also possible to replace condenser 33 by more elaboratefiltering means shouldthis be found necessary. It is evident that theplate current in tube 28 is a function of the instantaneous grid voltageas well as the instantaneous plate voltage, which latter is cyclicallyvaried by means of the induced voltage from the transformer secondarywinding. Thus as the duration of the 60- cycle impulses is only afraction of V second, it may readily be seen that the plate current intube 28 will vary in accordance with the phase relation between the60-cycle sine wave applied to transformer secondary winding 38 and the60- cycle impulses applied .to the control grid of tube 28. Thus adirect current regulating voltage is fgenerated; across resistor 32, themagnitude of which varies in accordance with the phase shift between the60-cycle sine wave and the squaretopped impulses. This voltage is fedthrough lead 3| to the control grid of regulator tube ll of the mastersine-wave oscillator l5, thus regulating its frequency and phase in sucha manner that the phase relation between the 60-cycle master sine Waveand the returning framing impulses automatically adjusts itself to thesame relation regardless of the length of leads 23 and 25, that is, thedistance of the scanner from the impulse generating equipment or, inother words, the phase delay incurred by the wire transmission.

While I have explained my method of television transmission inconnection withv some specific means, I am well aware that this methodcan be carried out by other means within the scope of the appendedclaims and I do not wish to be limited to the apparatus above described.

What I claim is:

1. In a televisionsystem, apparatus including a source of a mastersignal, a source of synchronizing signals and a phase comparator, atelevision scanner remote from said apparatus, means for transmittingsaid synchronizing signals to said scanner, means for returning saidsynchronizing signal from said scanner to said apparatus andspecifically to said phase comparator, means -i'or applying said mastersignal to said comparator, means for deriving from said comparator aregulating voltage in accordance with the phase difference between saidreturning synchronizing signal and said master signal, and means forcontrolling said source of synchronizing signals with said regulatingvoltage.

2. In a television system, apparatus including a source of a mastersignal, a source of synchronizing signals, said master signal and saidsynchronizing signals having the same frequency, and a phase comparator,a television scanner remote from said apparatus, means for transmittingsaid synchronizing signals to said scanner, means for returning saidsynchronizing signals from said scanner to said apparatus andspecifically to said phase comparator, means for applying said mastersignal to said comparator, means for deriving from said comparator aregulating voltage in accordance with the phase difierence between saidreturning synchronizing signals and said master signal, and means forcontrolling said source of synchronizing signals with said regulatingvoltage. I

3. In a television system including apparatus for generatingsynchronizing signals located at a first point and a television scannerat a second point remote from said apparatus, the method of operationcomprising the steps of generating synchronizing signals at said firstpoint, trans- .mitting said signals to said second point, returning saidsignals to said first point, and controlling the phase of said signalsat the point of generation in such a manner as to compensate for atleast a portion of the phase delay incurred by said signals intransmission between said points. 4. In a television system includingapparatus for generating synchronizing signals located at a first pointand a, television scanner at a second point remote from said apparatus,the method of operation comprising the steps of generating synchronizingsignals at said first point, transmitting said signals to said secondpoint, retuming said signals to said first point, and advancing thephase of said signals at the point of generation in such a manner as tocompensate for at least a portion of the phase delay incurred by saidsignals in transmission between said points. 5. In a television systemincluding separate apparatus for generating a master signal andsynchronizing signals, said apparatus being located at a, first point,and a television scanner located at a second point remote from saidfirst point, the method of operation comprising the steps of generatinga master signal and synchronizing signals at said first point,transmitting said synchronizing signals to said second point, returningsaid synchronizing signals to said first point, comparing the phases ofsaid master signal and said returning synchronizing signals, adjustingthe value of a regulating voltage in accordance with the phase shiftbetween said master signal and said returning synchronizing signals, andcontrolling the phase of said synchronizing signals at the point ofgeneration in accordance with said regulating voltage, so as tocompensate for at least a portion of the phase delay incurred by saidsignals in transmission between said points.

ULRICH KNICK.

